The present invention relates to pressure sensors.
In aviation or industrial fluid pressure sensing applications, fluids (pressurized media) can corrode metal sensing films. Metal sensing films are thus preferably placed inside a pressure sensor body and connecting leads are preferably fed through the body in such a way that corrosive process fluids do not come in contact with the sensing films and connecting leads. Corrosive process fluids can include gasses in an aerospace or stationary turbine engine, acids, caustics, oils, petrochemicals, and the like.
Alumina is a preferred material for sensor bodies because it has excellent mechanical properties and corrosion resistance. It is, however, difficult to bore vias in alumina for connecting leads between a sensing film and an external electronic circuit. Alumina sensors are preferably assembled by direct bonding. With direct bonding, mating surfaces of alumina layers are optically flat, clean and fully in contact with one another, and no bonding substance is used between layers. Any irregularity, such as a metal film feedthrough at the mating surfaces, would hold the mating surfaces apart by a microscopic amount and interfere with the direct bonding.
For demanding industrial, aerospace and turbine applications, an easily manufactured feedthrough seal is needed that does not degrade the high performance of a direct bonded alumina pressure sensor.
In the present invention, a feedthrough seal is formed by passing leads through a gap at a stepped corner between direct bonded layers of alumina and then filling at least a portion of the stepped corner with a seal that fills the gap.
The pressure sensor includes a beam with a blind end pressurized by fluid and an opposite end shaped to provide the stepped corner with the gap opening at the base of the stepped corner, where the gap is isolated from the fluid. The beam is formed around a central channel that opens through the gap at the isolated end. Sensing film that has an electrical parameter that varies with pressure is placed in the channel. The sensing film connects to the leads that extend out through the gap. The seal fills the gap around the leads and fills a portion of the stepped corner, sealing the channel. The beam including the blind end is integrally formed.